This invention relates to gas-metal-arc welding process by which a vertically downward weld deposit bead can be produced. The process involves continuously feeding a consumable or meltable electrode wire towards the weld deposit, utilizing a shielding gas flowing around the end of the electrode and the arc gap, to produce a plasma field in the gap. This process, by controlling and appropriately positioning the plasma field and causing a globular free-flight transfer for depositing metal from the wire upon the weld pool or deposit, permits welding downwardly, i.e. moving the welding wire downwardly, without run-off of the molten metal due to gravity.
In prior, generally vertically arranged weld beads, the procedure for applying the weld involved depositing the metal in an upward direction. That is, weld material has been applied upon the substrate and molten material applied upon the "shelf" or upper end of the weld bead so that the bead is gradually built upwardly. The prior system is relatively slow and presents quality and penetration problems. Thus, this invention is an improvement to the prior upward welding system for forming generally upright or vertical welds.
The general process involved, that is, the utilization of a shielding gas comprising a four-gas mixture, with a consumable wire electrode and the production of a hot plasma field within which the weld metal transfer occurs, is disclosed in my prior U.S. Pat. No. 4,463,243, issued July 31, 1984, for a "Welding System." Said process is additionally and further described in my subsequent U.S. Pat. No. 4,572,942, issued Feb. 25, 1986, for a "Gas-Metal-Arc Welding Process." In addition, the process may utilize a welding gun, such as disclosed in my prior U.S. Pat. No. 4,464,560, granted Aug. 7, 1984, for an "Arc Welding Gun With Gas Diffuser and External Cooling Conduit" to John G. Church and Emerson G. Malone. Further, a suitable welding gun and this kind of process is further disclosed in U.S. Pat. No. 4,529,863, issued July 16, 1985, for a "Gas-Metal-Arc Welding Method" to John-Claude Lebel.
The process disclosed in these prior patents produced a high rate of deposition of weld material which rapidly forms high-quality weld beads. The rate of metal deposition, the speed of formation of the bead and the quality of the bead all are substantially improved as compared with earlier welding processes. However, my U.S. patent application, Ser. No. 190,309, filed May 4, 1988, for a "High Rate Deposition Gas-Metal-Arc Welding Process" discloses a generally similar process but achieving substantially higher rates of speed for forming weld beads.
In this present application, I have discovered a process for producing, at relatively high deposition rates, weld beads in a downward direction, that is, by moving the welding wire, with the welding gun, downwardly, as compared to the prior processes utilized for forming verticaltype welds, namely, upwardly. This present, downward procedure produces high-quality welds with better penetration and much greater speeds of formation than that previously achievable through the conventional upwardly formed beads.